The basal ganglia constitute one of the most ancient and stable features of the vertebrate telencephalon. Dysfunction of the basal ganglia has been related to diverse ailments including parkinsonism, chorea, athetosis, chronic alcoholism and drug addiction. The proposed research program has as its key objective application of the comparative approach to study of the functional relationships of the basal ganglia in the vertebrate nervous system. In mammals the basal ganglia do not appear to constitute a major system independnet of the neocortex. In avian forms, however, the major projection of the basal ganglia, while also to nuclei comparable to those of the thalamic ventral tier, is not relayed back to the telencephalon but rather to the optic tectum. It is therefore hypothesized that in avian forms the basal ganglia exert their principal effects on behavior by modulating the timing and release of tectal-mediated orienting responses. A series of anatomic, electrophysiological and neurobehavioral experiments are proposed in order to test this hypothesis and clarify the role of the basal ganglia in the neural control of behavior. Anatomic experiments include mapping input the avian basal ganglia and its target cell groups by means of horseradish peroxidase histochemistry. Comparison of the organization of this system to those of mammals will be made. Electrophysiological experiments include stimulation-recording experiments involving unit recording from basal ganglia and thalamus while stimulating the ansa lenticularis. The ultimate physiological influences of the avian basal ganglia on its target cell groups and on the optic tectum will be determined. In addition, a neurobehavioral research program will be initiated in which chronic multiple unit recordings will be obtained in freely moving pigeons from units in the basal ganglia circuit.